Predistortion has been known as a technique for giving an inverse characteristic to an input signal of a circuit having a nonlinear input-output characteristic to thereby linearize an output signal of the circuit. A distortion compensation device using the predistortion technique has an estimation block which updates a transfer function of a predistorter in accordance with a nonlinear circuit which is the target.
Two inverses, i.e. post-inverse and pre-inverse, are present as inverse system characteristics for linearizing a nonlinear system. The post-inverse is a system characteristic which is placed after the nonlinear system to linearize an overall input-output characteristic. The pre-inverse is a system characteristic which is placed in front of the nonlinear system to linearize an overall input-output characteristic. An input-output characteristic which should be originally provided in the predistorter using the predistortion technique is the pre-inverse system characteristic.
However, since it is strictly difficult to obtain the pre-inverse system characteristic, a post-inverse system which can obtain a characteristic comparatively easily has been heretofore often used instead. For this reason, there is a problem that the thus obtained linearization characteristic is limited. In addition, the predistorter using the post-inverse system may generate an unstable signal with an extremely large amplitude when the gain of the nonlinear circuit as the compensation target changes. This incurs serious damage to the target nonlinear circuit.